One more thing:
The searches below state that they refer to bank accounts, it seems to me it is wrong. These seems to be phone directories instead; there is only a phone number but no account number. I haven't checked all PKO files but the error might be consistent.
I don't know how to get to the title pages to find out these books titles.
Cheers
Steven

I have moved your question to its own separate topic. These are definitely lists of bank accounts. The numbers you see, like 604 667 for Turobojski Czeslaw, are the bank account numbers. They are not phone numbers.